The 18-year-old burst onto the scene last season by scoring four goals in his first two senior appearances and eight in 18 overall, culminating in a spot in the Three Lions' Euro 2016 squad.
Ibrahimovic, who joined the Red Devils in July, told Sky Sports News: "I see Rashford as a huge talent, I have been here two weeks and I also saw him last season.
"I get to see him live every day now and he is the future of England. He just needs to keep working hard, keep focusing and everything will come by itself."
Man Utd boss Jose Mourinho had previously described Ibrahimovic, a free transfer after leaving Paris Saint-Germain, as a "gift" for Rashford.